Field of the Invention
Embodiments of the present invention generally relate to a read path of a hard disk drive (HDD), and more particularly to extending a read bandwidth and increasing a high-frequency signal-to-noise ratio (SNR) of a front-end of the read path.
Description of the Related Art
In magnetic recording HDDs, the read/write head is formed on an air-bearing slider that rides on a thin film of air above the rotating disk. A mechanical suspension comprised of a flexure with a gimbal at its end connects the slider to an actuator arm of the disk drive. The slider is attached to the gimbal, which allows for slight movement on the air bearing as the disk rotates. A transmission line provides electrical connection from the read/write circuitry, typically in a read preamplifier/write driver module or chip, through a short flex cable and suspension to the read and write elements on the slider.
A suspension that integrates the mechanical connection with the electrical connection is called an integrated lead suspension (ILS) that is connected between the flex cable and connection pads on the slider. A typical ILS is a generally flexible laminate of a conductive metal substrate like stainless steel, an insulating dielectric layer like polyimide, and electrically conductive copper lines or traces patterned on the dielectric layer. The transmission line for the signals from the read head to the read preamplifier thus comprises electrically conductive traces on the flex cable and the ILS.
The read/write head may comprise two devices: a read transducer and a write element. In newer HDDs, read transducers may continue to increase in impedance value as the transducer size may decrease as required by higher areal density. This impedance increase may result in two major drawbacks. First, high sensor impedance with accompanying parasitic capacitance may reduce the read bandwidth. As data rates continue to increase, the bandwidth must also continue to increase. Traditionally, the write path was the bottleneck to achieving higher data rates, but with higher read transducer impedance values, the read transmission path must improve to achieve higher data rates. Known solutions include lowering the impedance of the read path (i.e., higher cost) and/or lowering the input impedance of the amplifier.
As a second drawback, higher transducer impedance may also give more severe impedance mismatch between the transducer and the interconnect, which may result in a higher electronic noise contribution at high frequencies, therefore, an SNR degradation. The conventional solution requires higher cost and low noise electronics, or higher cost interconnects to achieve higher data rates for the read path.